In a computer system, a display screen is utilized for viewing data that the system user is currently interacting with. The data may comprise graphical data (e.g. a picture of an object) or textual data (e.g. a document). The picture is typically viewed within an area defined within the screen, referred to as a window. The window may be as large as the screen or may be made smaller depending on the particular needs of the user. FIG. 1 illustrates a typical window 10 within a display screen 20. Most times, all of the data will not fit within the window or screen. As a result, only a portion of the data can be viewed by the user at one time. In order for the user to be able to display other portions of the data, the view of the picture in the window needs to be changed. To change a user's view the picture must be manipulated in some way by the user. There are two common view changing methods: the position controlled method and the rate controlled method.
An example of a position controlled method for changing views of a picture is seen in many graphical programs. This type of method commonly employs a "grabber" tool which may be selected from a menu of tools. The menu of tools is typically displayed on the side of the window. Once the "grabber" tool is selected, a "grabber" tool cursor, (sometimes in the shape of a hand), is displayed on the screen. The computer system's input/output (I/O) interface (e.g. a mouse) controls the movement of the cursor within the screen and also allows the user to interact with the data on the screen. When the I/O interface is deactivated, (e.g. when the mouse button is up), the I/O interface only controls the movement of the cursor within the screen. When the I/O interface is activated, (e.g. when the mouse button is down) the user is able to directly interact with the data on the screen.
View changing with the "grabber" tool is achieved by holding down the mouse button (i.e. activating the I/O interface) while dragging the mouse in an arbitrary direction and then releasing the button (i.e. deactivating the I/O interface); leaving the cursor in a new position on the screen. These actions cause the cursor to effectively "grab" onto the picture and scroll it in the direction of the mouse movement.
A rate controlled view changing method employs scroll arrows 30 located at the border of a window 10 (refer to FIG. 1 ). By positioning cursor 12 on any of the arrows 30 and holding the mouse button down, the view will continuously move in the direction of the arrow. For instance holding the right scroll arrow down, will move the view (not the picture) continuously to the right, effectively scrolling the picture to the left. The rate of scrolling is fixed by the application program of which the scrolling tool is within. Note that the view can only be scrolled in four directions--up, down, left, and right. For example, it is not possible to move the picture diagonally as with the "grabber" tool.
The "grabber" tool and the scroll tool provide two distinct styles of view changing. The "grabber" tool is characterized as a positional controller because the change in the cursor position controls the change in position of the picture being viewed. Usually, there is a one-to-one mapping so that the picture is moved the same amount as the cursor movement. This effectively gives the impression that the user can "grab" onto the picture and slide it within the window directly. Thus, the grabber tool is desirable because it allows the user to have a localized fine scrolling control by being able to move the picture with the cursor. The grabber tool is less effective when scrolling large distances, since the user would have to typically do multiple "strokes" with the mouse to cover the distance.
The scrolling tool, on the other hand, is useful in that once the mouse button is depressed over a scroll arrow, the picture begins to scroll at a fixed rate. The picture continues to scroll while the mouse button is held down. Thus, the scroll option is desirable because it allows continuous scrolling without the effort of doing multiple "strokes" with the mouse, unlike the "grabber" tool. However, since the scroll steps are typically fixed, it is usually not possible to have the fine tuning control such as that of the "grabber" tool. In general, the "grabber" tool provides a finer localized control whereas the scroll tool provides a faster but coarser control. Both types of controllers offer their own unique and useful manner in which to change views of the picture within a window.
The manners in which the scrolling and grabber tools are selected are distinctly different too. The scroll tool is typically available at all times when the window is open. As shown in FIG. 1, the scrolling arrows are always displayed while the user is manipulating the picture. As long as the mouse pointer is moved over a scroll arrow, it can be clicked to perform scrolling. The grabber tool on the other hand needs to be initially selected from a palette of tools typically located along the side or top of the window. In other words, the user must consciously select the grabber tool in order to use it. To do this the user must take two additional steps: 1) move the mouse to the grabber tool select button on the palette and 2) depress the mouse button. The user must interrupt current ongoing screen interaction to do this.
What would be desirable is a way to give the user the ability to switch between two different viewing methods without having to interrupt picture manipulation activity. In this way the user would be given increased viewing flexibility.